Re: [ATM] A powered alt-az ground-board

["Don Clement" <don_clement@charter.net>]

Jerry,

Gabba Gabba Hey!

IMO it is easier to filter a low frequency low voltage pure sine AC
transformer arrangement with known harmonic components than filter the
unpredictable noise components of a brush slip ring.  Also ferrites work
well for filtering high freq components at I/O & power lines of a CCD.

BTW there are really no DC fan motors. DC motors are actually a very noisy
type of AC motor that either have a commutator or an electronic commutator,
both of which create electrical noise  and  plenty of harmonics when motor
currents switches rapidly. AC fan motors are quieter wrt electrical noise
generated especially 3 phase AC motors that have none of the fast switching
currents generating harmonic components found with  so-called DC motors.



Don



----- Original Message ----- 
From: "Jerry" <wa4guu@verizon.net>


Gabba gabba...

I think without an iron core that would complicate the mechanics of relative
rotation between the coils, the efficiency would be poor. The increased
power required might make it not so good a trade if you are running on
batteries. May as well mount the batteries on the rocker box.

But if it's getting power from the grid some inefficiency might not be a big
problem. But you still have a run a power wire to the ground board from the
AC source, or a wire to provide DC from external batteries to a ground board
mounted inverter to provide AC to the ground board/rocker box transformer.
Depending on how many things you are powering all that inefficiency might
put a fair amount of heat right under the telescope.

Rather than using a transformer, I would go with DC through contact rings
and brushes and if necessary, filter any brush noise on the telescope side
of the connection. But better still is to mount a battery on the ground
board and have the scope and its power in one package. The altitude motion
is not going to wrap the wire in a coil.

Another concern I would have if I were doing imaging with a CCD is the
possibility of the AC interference with the camera. I think the AC voltage
required to get enough power through the transformer (enough to make me
happy) might be rather high.

If your ground board and rocker box were big enough you might be able to
make a large enough capacitor by putting two circles of foil on each to get
enough power through. And the good thing about that is that your truss tube
telescope is also a bug zapper. And a bad thing is now you need more power
for the fan that blows the dead mosquitoes off the mirror. Crank the source
AC voltage up to make up for that.

Jerry

-----Original Message-----
From: Don Clement


Perhaps a better method of transmitting power through a rotating mechanical
joint than using the direct contact (and  noisy) slip ring would be to use
non-contact magnetic induction and AC current through a pair of coils. The
ac power could be easily rectified and filtered to DC on the scope end.



Don Clement

Running Springs, California






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